1. Field of the Invention
The present invention relates to a control apparatus of a fuel supply system which directly injects fuel into a combustion chamber, i.e. a cylinder, of a motor gasoline internal-combustion engine or the like.
2. Description of Related Art
A cylinder injection type fuel control apparatus which directly injects fuel into a combustion chamber of an internal-combustion engine is expected to provide primarily four advantages set forth below.
(1) Reduced harmful substances contained in exhaust gas
In a conventional type which injects fuel in an intake pipe, i.e. outside a cylinder, a part of the injected fuel adheres to an intake valve or the interior of the intake pipe before the injected fuel is introduced into the combustion chamber, i.e. inside the cylinder, causing a delay in the supply of the fuel into the cylinder. This makes the vaporization of the fuel difficult, frequently leading to the emission of a harmful substance (CO, HC) at the time of startup in low temperature or during a transient operation requiring a quick response.
In the case of the cylinder injection type, since fuel is directly injected into the combustion chamber, i.e. cylinder, there is no such delay in fuel supply as described above, so that highly precise air-fuel ratio control can be achieved. Thus, harmful substances contained in exhaust gas can be reduced by carrying out ideal combustion.
(2) Reduced fuel consumption
When injecting fuel into a cylinder, stratified charge combustion, wherein combustible fuel is formed around a spark plug at the time of ignition, is possible; therefore, combustion can be implemented with less fuel with respect to the amount of air introduced in the cylinder as compared with the stoichiometric ratio.
Furthermore, the successful stratified charge combustion reduces the deterioration in combustion attributable to the exhaust gas recirculation (EGR), enabling more EGR to be implemented. This feature coupled with the reduction in pumping loss permits improved fuel efficiency.
(3) Greater output
Since the combustible fuel gathers around a spark plug due to the stratified charge combustion, the end gas, which is a fuel-air mixture remaining due to the delay in combustion and which causes knocking, is decreased with resultant good anti-knocking performance. Hence, the compression ratio can be increased, leading to greater output.
Since the heat of the introduced air is removed when the fuel injected into a cylinder vaporizes, the volumetric efficiency owing to an increase in the volume density in the cylinder can be improved, leading to greater output.
(4) Improved drivability
Since fuel is directly injected into a cylinder, a total delay accumulated during the process, wherein the fuel is supplied, ignited, and burnt to produce output, is smaller as compared with the case of a conventional non-cylinder-injection type engine, thus making it possible to achieve an engine which responds more quickly to the operation performed by a driver or a request from the driver.
Hitherto, diverse inventions on direct injection type spark ignition engines have been proposed in the field of cylinder injection type fuel control apparatuses.
Japanese Unexamined Patent Publication No. 60-30420 has disclosed a cylinder direct injection type spark ignition engine adapted to advance fuel injection timing as load increases. In this engine, while the engine is running with low load, fuel is injected in the vicinity of a spark plug during the latter half of a compression stroke to form a combustible fuel-air mixture in the vicinity of the spark plug so as to ensure good ignition and combustion. While the engine is running with high load, fuel is injected in the first half of the suction stroke to fully disperse the fuel in a cylinder so as to enhance the coefficient of use of air thereby to attain greater output.
Japanese Unexamined Patent Publication No. 2-169834 has disclosed an invention on a cylinder direct injection type spark ignition engine which is capable of injecting a required amount of fuel by dividing it for the suction stroke and the compression stroke according to the operating state of the engine. More specifically, the all required injection amount of fuel is injected in the compression stroke to form a stratified fuel-air mixture which permits ignition and combustion if the required fuel injection amount is a first injection amount or less, which first injection amount being a sum of the minimum compression stroke fuel injection amount permitting the formation of an air-fuel mixture which can be ignited by a spark plug, and a minimum suction stroke fuel injection amount which enables ignition flame to propagate when the fuel evenly disperses in a cylinder. If the required fuel amount is not more than a second injection amount that is the minimum fuel injection amount which permits the formation of a homogeneous fuel-air mixture which can be ignited by a spark plug, and not less than a third injection amount that exceeds the first injection amount, then the required injection amount is injected by dividing it for the suction stroke and the compression stroke so that the fuel injected in the suction stroke forms a lean fuel-air mixture for flame propagation in the whole cylinder, while the fuel injected in the compression stroke forms a relatively rich fuel-air mixture in the vicinity of the spark plug.
FIG. 15 shows a block diagram of an internal-combustion engine disclosed in the foregoing Japanese Unexamined Patent Publication No. 2-169834. The internal-combustion engine is equipped with an engine main body 11, a surge tank 12, an air cleaner 13, an intake pipe 14 connecting the surge tank 12 and the air cleaner 13, an electrostrictive type fuel injection valve 15, a spark plug 65, a high-voltage reservoir tank 16, a high-voltage fuel pump 17 in which the discharge pressure thereof for forcibly feeding high-pressure fuel to the reservoir tank 16 via a high-pressure conduit pipe 18 can be controlled, a fuel tank 19, a low-pressure fuel pump 20 for supplying fuel from the fuel tank 19 to the high-pressure fuel pump 17 via a conduit pipe 21, a piezoelectric element cooling inlet pipe 22 for cooling the piezoelectric element of the fuel injection valve 15, a piezoelectric element cooling return pipe 23, and a branch pipe 24 for connecting the high-pressure fuel injection valve 15 to the high-pressure reservoir tank 16.
An electronic control unit 40 has ROM, RAM, and CPU which are connected using a bidirectional bus; it is provided with an input port 25 and an output port 26. The electronic control unit 40 receives a detection signal of a pressure sensor 27 which detects the pressure in the high-pressure reservoir tank 16, an output pulse of a crank angle sensor 29 which generates an output pulse that is proportional to an engine speed Ne, and an output voltage of an accelerator lift sensor 30 which is generated in accordance with a lift .theta.A of an accelerator pedal.
The conventional cylinder injection type fuel control apparatus is configured as set forth above, and it has been posing a problem in that the internal-combustion engine fails to operate properly if the fuel supply system, especially a high-pressure fuel system including the high-pressure fuel pump 17 and the high-pressure conduit pipe 18, incurs a failure.
A cylinder injection type fuel control apparatus has been proposed which has a low-pressure fuel system and a high-pressure fuel system so as to change a low-pressure control mode over to a high pressure control mode upon completion of startup; however, it has been posing a problem in that, if the pressure of fuel fails to reach a high level in the high pressure control mode following the startup, e.g., if a fuel system including the high-pressure fuel pump and a fuel pressure switching solenoid fails, then the valve opening time will be too short for the fuel pressure and an inadequate amount of fuel is supplied, preventing the drive because the engine fails to work properly.